The present invention relates to medical devices in general, and in particular to systems for performing myocardial revascularization.
Myocardial revascularization is a surgical technique whereby small holes or craters are created in the myocardium to allow oxygenated blood within the ventricle to contact the myocardium. One technique, called transmyocardial revascularization (TMR), involves routing an energy delivery catheter through an opening in the chest wall to the exterior of the patient""s heart muscle. Ablation energy is then delivered to the catheter to create a hole that extends from the epicardium, or exterior of the patient""s heart, to the interior of the ventricle such that oxygenated blood flows into and out of the holes. These holes rapidly seal at the outside of the heart but remain open towards the interior of the ventricle. Another technique, called percutaneous myocardial revascularization (PMR), utilizes an energy delivery catheter that is routed through a patient""s vasculature to the interior wall of the left ventricle. Ablation energy is then supplied to the ventricular wall to remove a portion of the endocardium and expose a portion of the myocardium to oxygenated blood flow.
Myocardial revascularization is most often used when an area of the myocardium is not receiving adequate blood flow because of clots or diseases that inhibit the ability of the vessels to supply blood to the heart. It is not known whether the procedure induces new blood vessels to form in the myocardium or simply deadens nerve endings in the myocardium to alleviate patient discomfort.
Not all cardiac tissue can be helped using myocardial revascularization. For example, if the myocardial tissue has been deprived of oxygenated blood for too long, it may be dead and no benefits to the tissue will be obtained if treated. Applying ablation energy to such myocardial tissue is not only a waste of time, but the tissue may be more susceptible to ventricular perforation. To increase the efficiency and efficacy of a myocardial revascularization procedure, there is a need for a system that can guide a physician to only perform a myocardial revascularization procedure in viable cardiac tissue.
The present invention is a method and apparatus for limiting the delivery of ablation energy to viable areas of the myocardium. An energy delivery catheter is routed to the patient""s myocardium. A determination is made if the myocardium adjacent to the distal end of the catheter is viable and, if so, ablation energy is delivered through the catheter to the myocardial wall. If the tissue adjacent the distal end of the energy delivery catheter is not viable, then no ablation energy is delivered.
In one embodiment of the invention, tissue viability is determined by applying a test signal to the tissue and measuring the impedance of the tissue in response to the test signal applied. If the impedance is greater than a predefined amount, the tissue is deemed not to be viable. Therefore, no ablation energy will be delivered.
The energy delivery catheter may be routed through the patient""s vasculature or through an opening in the patient""s chest wall.